An embodiment relates to video processing.
Flickering is the apparent fluctuation of light in video, at a local or global scale. Flickering is due to the presence of non-uniform light source(s) in the imaged scene: when a camera captures successive frames of a scene which is illuminated by a light source which intensity varies in time, the pictures will appear (locally or globally) alternatively dark (low intensity illumination) and bright (high intensity illumination). Typically, all artificial lights are powered by either alternating current (AC)—which varies continuously as a sines law with period T or pulse-width modulated (PWM) current—which alternates between ‘on’ and ‘off’ modes in a discrete way. While flickering due to light sources powered by AC current can be attenuated relatively easily (by adjusting the exposure time of the acquisition system to be a multiple of the known period T), it is much more difficult to mitigate the flickering effect when the light source is PMW. As a consequence, the observed flickering/flashing appears as an artifact in the video. This artifact can be particularly disturbing insofar as it may convey a wrong information (e.g., flashing is often the signal of distress, or used to capture attention). It is noted that this phenomena is also related to the relatively short exposure time (˜ms) of the video acquisition system (at least shorter than the duty cycle of the PWM illuminant). Conversely, the human eyes integrate the visual information over time, and this is why most people are oblivious to fluctuating light sources in their environment.
Video capture devices are becoming ubiquitous and have a wide range of applications, from video camera surveillance in public or private places, to on-board systems in robotics applications. For example, image capture devices are being utilized on vehicles to capture the environment about the vehicle. Surround view cameras (backup, front-viewing, side-viewing), are or will become a standard in vehicles. Similarly, PWM lightings, in particular Light Emitting Diode (LED) lights, are more and more ubiquitous in public and private places, due to their low cost and high robustness.